6.(C is uncertain, so there are two possibilities) Suppose that C is based on the maximum angle from the big side to the big corner. Because the acute triangle, C2 < a2+B2-C2-5 < 0(- root number 5, positive root number 5)- must be a positive number, so (0, positive root number).
But b > a b may also be the largest angle, but it must be an acute angle, so B2 < A2+C2-similar to the above.
Finally, (root number 3, root number 5)
15, (1) tanc = tan {180-(a+b)} =-tan (a+b) = calculate tanc by yourself with the formula and then calculate ∠C with the range (0, π) of the interior angle of the triangle.
Other topics are not clear.
I just finished my senior one and looked at these topics. These topics are relatively basic. If you have finished the first year of high school, it's time to cheer.